This invention relates to preparation of food, and more particularly to an apparatus for pressure cooking food items in microwave ovens.
Pressure cookers are well known for their capacity to impart a highly desirable tenderness, texture and flavor to certain prepared foods, particularly meat. Pressure cookers usually include a bowl-shaped container or base open at the top for receiving food, and a top cover for closing the container. Because they utilize a positive pressure, these appliances must be equipped with certain features not required by other cooking utensils. For example, means must be provided for maintaining the container and cover in a fluid sealing engagement for maintenance of positive pressure. A valve is needed for maintaining a selected level of positive pressure. The cooker also should have a back-up pressure release valve, in case there is a malfunction in the pressure regulating valve. Finally, it is desirable to have auxiliary valve means for preventing positive pressure build-up unless the cover and container are properly engaged, and for rapid pressure release in the event of an attempt to open the pressure cooker prior to a sufficient release of positive pressure.
A pressure cooker container and top may be threadedly engaged, as disclosed in U.S. Pat. No. 4,490,597 to Mengel granted Dec. 25, 1984. A more convenient opening and closing arrangement is shown in U.S. Pat. No. 2,622,187 to Welch granted Dec. 16, 1952, in which the container and cover each are provided with ledges, which interlock with one another responsive to rotation of the cover. A gasket is provided to complete the seal. Welch utilizes the cover weight as a pressure regulator valve, while Mengel discloses a spring loaded regulator valve. Mengel also shows a safety relief button which, when pressed by the user, vents the pressure cooker.
U.S. Pat. No. 4,024,982 to Schultz granted May 24, 1977 discloses a ring rotatably mounted with respect to the cover or lid of a pressure cooker. The ring is equipped with handles for rotating it 180.degree. between its open and closed positions. A valve seating, mounted in the lid, has a valve cone that remains open until the ring is rotated to the closed position, thus to prevent a pressure build-up unless the cooker is properly closed. An alternative structure, shown in U.S. Pat. No. 4,103,801 to Walker granted Aug. 1, 1978, includes a sealing plug in a cover vent opening. The plug is positioned so that it can rise to permit a pressure build-up only when a lock member is in its proper position.
Pressure cookers designed for use in microwave ovens are intended to afford the above-mentioned advantages of pressure cooking along with the convenience and speed of microwave cooking. These advantages give rise to certain structural requirements not heretofore adequately addressed. For example, it is desirable in microwave pressure cooking to construct the container and cover of a microwave permeable material. Yet, such materials do not lend themselves to the positive yet convenient closure desired for pressure cookers. The valves presently used to prevent pressure build-up prior to a proper seal are more complex than necessary, and often utilize metal springs and other components not suitable in microwave environment. Moreover, the characteristically smaller size of microwave pressure cookers raises the need to ensure that large, flat, bulky food items, for example lettuce and cabbage, do not interfere with operation of the pressure regulator valve or safety pressure release valve.
Therefore, it is an object of the present invention to provide a means for the convenient and releasable sealing of a pressure cooker cover and container, particularly when these components are constructed of a microwave permeable material.
Another object of the invention is to provide a simple and reliable means to prevent positive pressure in a pressure cooker chamber unless the cover and container are correctly engaged.
Another object is to provide a means for rapidly releasing pressure from a pressure cooker during an attempt to disengage the cover and container before the positive pressure has subsided.
Yet another object is to provide structure for preventing food items in a pressure cooker from blocking or otherwise interfering with pressure relief openings.
And, it is an object of the present invention to provide a pressure relief valve and auxiliary safety valve which are easily removed from the pressure cooker for inspection or cleaning.